In the manufacture of glass articles in glassware forming machines, as example the one called I.S. machine, the articles are formed in molds manufactured of cast iron, regularly from "gray iron", and this is so because of this physical properties, ease of machinability, thermic conductivity and functional and economical considerations.
However, one of the main problems of the molds of the previous art is that has not been possible to uniform the transference of heat between the molten glass and the mold, which it itself produces cracks or checks of thermal origin in some sections of the formed articles and/or an uneven distribution of the glass.
This type of problem is mainly influenced by the mold's operating temperature, which must be kept in a condition of quasi-static equilibrium, this is, subject to heating-cooling cycles which maintain the ideal temperature of the mold in accordance with the type, shape and size of the article that is being manufactured.
Another problem of the molds of the previous art, is that, due to the high speed of operation of the forming machines, the molds absorb heat at a much greater speed than the dissipated heat. This implies that the mold is exposed to a, shorter time cooling period before the next gob or preform of molten glass is loaded into the molds.
At present, there already are patents for cooling systems that dissipate the heat that is absorbed by the molds during the glass article manufacturing process, for example, U.S. Pat. No. 3,666,433 of H. Nebelung et al, shows a mold that is cooled by air that includes a thermocouple located in the intermediate part of said mold and a section that is heat sensible. A control system that includes a damper valve for controlling the flow of cooling air in response to the output of the thermocouple.
Other arrangements for cooling molds, wherein the main cooling fluid is air, are described in U.S. Pat. Nos. 3,888,647 of Breden et al; 4,361,434 of Schneider; 4,388,099 of Hermening et al; 4,502,879 of Foster; 4,525,191 of Fenton; and 4,578,014 of Jones.
However, one of the main problems of the molds that are cooled with air, is that in order to effect a better heat transfer, it is necessary to increase the heat transfer area in the mold (which has been developed into very complex solutions) or in increasing the flow of the cooling air. In last case, the increase of the air speed is limited by the excessive noise that is provoked within the plant. In any case, the high speed of operation of the forming machines results in that even these solutions are not commensurate with the cooling needs required by the molds.
Notwhistanding with the above wherein is mentioned that several developments are used in order to improve the transference of heat between the glass and the mold, it is still not possible to remove or liberate the heat from the article in a uniform and controlled manner. This type of problem is partly due to the variations in thickness of the internal walls of the mold (due to the profile of the article), and this causes that the heat loss be faster in some sectors of the mold that in others. The difference in the thickness of the walls of the mold cause a different temperature profile in the article being manufactured (in a radial as well as an axial manner), which make difficult the compensation of the change which are inherent to the glass article manufacturing process, such as the change of ambient temperature, the temperature and weight of the glass, etc.
Another problem that has been present in the glass article manufacturing process is the irregularity of the walls of the glass articles.
An additional problem to those already cited is the duration of the molds. Due to the fact that the mold is exposed to rapid cooling, thermal gradients are generated and these tend to cause different dilation in keeping with the distance from the surface, and this in turn generates thermal strains in the mold's material which eventually give place to mold cracking.
Taking into account the defects of the previous art, the present invention refers to a cooling method and mold arrangement for the manufacture of glass articles or similar materials, which uniforms the heat extraction between the molten glass and said mold (the cooling being independent of the thickness of the mold's walls).
Some other advantages of the present invention are:
Improve the distribution of glass in the mold due to uniform extraction of heat. PA1 Increase the production velocity of the articles that is being manufactured. PA1 A greater resistance to the article's internal pressure. PA1 A reduction of manufacturing defects due to cool or hot molds. PA1 It provides an increased lifespan of the molds which in turn prevents areas that are overheated.